1. Field of Invention
This invention relates to railroad car trucks and more particularly to an improved connection between the truck side frames and the truck bolster.
2. Prior Art
Modern railroad car trucks used to support a body of a railroad car are commonly referred to as a 3-piece truck. The truck includes a pair of wheelsets having axle ends journaled in bearings positioned in pedestal jaws formed at ends of a pair of spaced side frames. Each side frame in turn has a centrally located window in which a set of springs carries ends of a transversely positioned bolster. The springs cushion vertical movements of the bolster which in turn supports the railroad car body.
Connections between the bolster ends and side frames most often include sets of friction shoes to dampen vertical oscillating movements of the bolster which are inherent with coil spring suspension. The friction shoes are carried in pockets formed back-to-back in each bolster end. This back-to-back positioning of the pockets results in a substantially reduced section modulus of the bolster between the pockets.
In addition to vertical movements of the truck bolster, the bolster also yaws and pitches in response to changes in direction during travel of the truck. These latter movements of the bolster are not cushioned and can result in contact between abutting structural members of the bolster and the side frame. Contact also occurs when the side frames pitch in response to irregularities in track height. The dynamic and static forces related to truck travel are of such a high magnitude that when contact does occur, stresses of high value are created. Because of the reduced section modulus of the bolster between the friction shoe pockets, this portion of the bolster may be stressed close to or even beyond its yield point. Thus, the bolster can become subject to fatigue failure and permanent deformation.